I’m interested in the Main Effects of Group and Time and the Interaction between them
model <- lmer(Y~ Group * Time +(1|ID),data=data)

Variables:
Time (Day1, Day2)
Group A B C

First I thought that there is no Random Effect Variance of ID, but to me in the plot it looks like there is dependency in the cluster. Could the problem lay in the small cluster size of only 2 Time points? What would be a more appropriate way to model the problem?
enter image description here

I tryed fitting a mixed model where I got the result from.
A normal linear model shows no significant correlation between Group, Time and Y.